1. Field of the Invention
The present invention relates to a two-input/two-output active selector switch with distributed structure. The invention can be applied especially to digitally controlled phase control devices. These devices are used for example in telecommunications or in broadband microwave instrumentation. They are also used particularly in electronically scanned type antennas. The invention belongs especially to the field of microwave microelectronics and more particularly to the technology of microwave monolithic integrated microcircuits (MMIC).
A digitally controlled phase control device generally works on the basis of selection switching between at least two different channels, each capable of behaving either as a phase-shifter or as a line with programmable length. In practice in a phase shifter, between two states, the signal undergoes a phase shift in transmission where the value of the phase shift is constant in the frequency band considered. However, in a line of programmable length, between two states, the signal undergoes a phase shift in transmission where the value of the phase shift corresponds to the propagation of the current along a line of constant length (implying a constant delay) in the frequency band considered.
2. Description of the Prior Art
It is known that a phase control device comprises a digitally controlled input and, between a signal input and a signal output, at least one cell comprising passive selector switch means which are capable, under the control of a command input bit, of providing at least two different transfer functions in terms of temporal phase and/or delay. A phase control device of this kind can be implemented by means of a microwave monolithic integrated circuit (MMIC) technology in a frequency band ranging for example from 2 GHz to 18 GHz. However, the serial connection of several cells made entirely with MMIC technology leads to relatively great insertion losses. Indeed, a passive selector switch working in the frequency band that goes, for example, up to several tens of GHz is capable, in insertion, of losing 1 to 2 dB depending on the insulation.
Similarly, a phase-shift or delay cell may show losses of up to 2 dB for the medium significant bits (or mid-position bits) and the most significant bits. Thus, the making by MMIC technology of a line with a programmable length of 9 bits comprising 9 series-connected cells of the same structure may lead to insertion losses of between 30 and 40 dB.
This problem of insertion losses may be resolved by the use of active selector switches with distributed structure as described in the French patent application 98 16556. The active selector switches however have the advantage of combining the amplification function and the selection-switching function in overcoming the losses of a passive selector switch. These active selector switches are either switches with two inputs and one output, or switches with one input and two outputs.
It is an aim of the invention especially to enable the making of active selector switches with two input and two outputs. To this end, an object of the invention is an active selector switch comprising two distributed dual amplifiers. Each dual amplifier has an upper amplifier and a lower amplifier each having a drain line and a gate line that are common to them, the input E1, E2 of an amplifier being the free (or unconnected) end of its gate line and its output being the free end of its drain line, the inputs of the amplifiers forming the two inputs E1, E2 of the selector switch, the output of the two upper amplifiers being connected to form the first output S1 of the selector switch, the outputs of the two lower amplifiers being connected to form the second output S2 of the selector switch, the routing of the signal from an input to an output being controlled by the state of the amplifiers.
In another embodiment, a selector switch according to the invention comprises two parts, each part comprising a distributed-structure amplifier whose elementary cells comprise at least two cascode-mounted transistors. The state of each transistor in common source connection is controlled by applying the control voltage to its gate. The signal coming from one of the common-source transistors (the one switched over into the xe2x80x9conxe2x80x9d state) is then directed toward the common-gate transistor which is common to both common-source transistors in a shared cascode structure. The two inputs E1, E2 of the selector switch are the free ends of the gate lines of the two distributed transistors and the outputs S1, S2 of the selector switch are the free ends of these two amplifiers.
An object of the invention is also a phase control device comprising a selector switch of this kind.
The main advantage of the invention is that it enables the making of a two-input and two-output active selector switch that is both compact and economical.